Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $201.85   11.560%   $225.1839   $225.18   $225.20   $225.20  
  Purchase #2 $174.75   10.289%   $192.73   $192.73   $192.75   $192.70  
  Purchase #3 $90.77   5.292%   $95.5735   $95.57   $95.55   $95.60  
  Purchase #4 $17.69   11.503%   $19.7249   $19.72   $19.70   $19.70  
  Purchase #5 $53.97   13.650%   $61.3369   $61.34   $61.35   $61.30  
  Purchase #6 $204.77   13.784%   $232.9955   $233.00   $233.00   $233.00  
  Purchase #7 $29.84   5.469%   $31.4719   $31.47   $31.45   $31.50  
  7 purchase totals = $773.64       $859.0166   $859.01   $859.00   $859.00